Olefin polymers such as ethylene copolymers have been conventionally used as materials for hollow molded articles, extrusion molded articles, films, sheets, etc. One well known olefin polymerization catalyst for preparing these olefin polymers is a catalyst comprising a transition metal catalyst component such as zirconocene and an organoaluminum oxy-compound (aluminoxane). As the transition metal catalyst component used for this catalyst, for example, ethylenebis(indenyl)zirconium dichloride is known. Olefin copolymers obtained by using this transition metal catalyst component are characterized in that their molecular weight distributions are narrow and films formed from the copolymers are free from tackiness.
The properties required for the olefin polymers vary according to the use and the molding process thereof. In order to adjust the properties, the ratio between the comonomers has been conventionally controlled so as to alter the crystallization temperature, the melting point, etc. of the resulting copolymer.
In the use of the conventional catalysts, however, there is a limit to the alteration of the crystallization temperature and the melting point.
U.S. Pat. No. 5,279,999 discloses a catalyst composition obtained by contacting (a) a Group IVA metal compound of the general formula EQU (Cp).sub.p MeX.sub.4-p
(wherein Cp is, independently, cyclopentadienyl groups substituted with one or more hydrocarbyl groups, and at least one cyclopentadienyl group is substituted with a single, optionally substituted, aryl group. Me is a Group IVA metal, X is one or more non-cyclopentadienyl substituents attached to the Group IVA metal, wherein the substituents are hydrocarbyl groups, hydrocarboxy groups, hydrocarbamide groups, hydrogen or halogen, and p is an integer of from 1 to 4.) and (b) an aluminoxane for (co)polymerizing olefins.